The invention relates to a device for the variable actuation of the gas-exchange valves of internal combustion engines.
Such devices are used to configure the control the gas-exchanging valves, so that it is possible to operate reciprocating engines without the otherwise customary throttle valve.
Such a device is known, for example, from the DE 101 23 186 A1. For this device, a revolving cam initially drives an intermediate link, which carries out an oscillating, strictly rotational movement and carries a control cam, which is composed of a pause region and a lifting region. The control cam transfers the lifting cam, required for actuating the valve, to the roll of a cam follower-like power take-off element, which, in turn, actuates the valve. The desired, different valve-lifting cams are produced owing to the fact that the center of rotation of the intermediate link is shifted onto a circular path, which is concentric with the roll of the power take-off link in its position with the valve closed. The center of rotation is formed by a roll provided at the intermediate link, which is supported non-positively on a circular path in the housing, which is also concentric with the roll of the power take-off link, that is, forms a cam offset from the path of the center of rotation, and which is referred to as a gate. In addition, the roll mounted at the inter-mediate link, is supported at a radial cam, the angular position of which fixes the position of the center of rotation of its circular path.
Further devices of this type have become known, for which the center of rotation of the intermediate link, driven by the cam, is to be adjusted on a circular path (Offenlegungsschrift 195 32 334 A1; EP 0717 174 A1; DE 101 64 493). However, the prior publications do not teach the constructive realization of such an adjustment.
It is a common feature of all known devices that a separate adjusting device is required for adjusting the center of rotation of the intermediate link, driven by the cam. According to the state of the art, this adjusting device is constructed by an adjusting the cam shaft, which is mounted in the housing.
It is an object of the present invention to provide a device which, without a separate adjusting device, is constructed simply and with few components.
Preferably, the bolt, on which the intermediate link is mounted, is constructed simultaneously as an adjusting shaft For this purpose, it is provided with cam discs and is mounted freely rotatable or in hinged columns, in a four-bar mechanism or in a sliding element. The cam discs are fastened non-rotatably on the bolt. The cam discs are supported directly or indirectly at the housing. If the support is direct, sliding blocks of a material of greater strength may be provided in the housing for the cam discs. By rotating the adjusting shaft with a suitable adjusting agent, such as an adjusting motor, the desired valve lilting cam is set. Since the adjusting agent, such as an adjusting motor, usually is fastened to the housing, the bolt or control shaft, however, shifting during the adjusting motion parallel to itself, a connecting element must be disposed between the two, which permits this shifting. Depending on the space condition, this connecting element may be an articulated shaft, a Schmidt coupling, an Oldham coupling or also a gearwheel or chain gear mechanism. If the actuation is hydraulic, a lever mechanism is also available.
The inventive device, including an adjusting motor or an adjusting device, may be provided for all intake and exhaust valves of a cylinder head. If the intake and exhaust valves of a cylinder head are actuated by a common camshaft, the inventive device, including an adjusting motor or an adjusting device, may be provided for all intake and exhaust valves of a cylinder head. The inventive device, including its adjusting motor or an adjusting device may be provided separately for each valve of an engine, so that any combination of valve lifts or opening angles of the individual valves of an engine, including the switching off of individual cylinders, is possible. Usually, however, a common adjustment of several valves is provided. This is the case especially with multi-valve engines for the intake and exhaust valves of a cylinder. For example, two intake valves may be actuated by a cam over an intermediate link, which has a control cam for each valve. Since only one intermediate link and only one bolt are present, both valves are adjusted jointly and similarly. Pursuant to the invention, however, two different control valves may also be provided at the common intermediate link with the result that the two valves have different lifting cams, although they are adjusted jointly. Particularly in the lowest load range, this variation opens up the possibility of opening only one of the two valves. The special advantage of this possibility lies therein that, in the lowest load range, very small cross sections have to be opened up and this can be done more accurately, if they are opened up by only one valve. In addition, the possibility exists of producing a twist in the cylinder charge because only one of the intake valves is opened. The possibility of producing different valve lifting cams for two intake or also exhaust valves of a cylinder are expanded pursuant to the invention owing to the fact that two different cams and two different intermediate links with different control cams are used. Nevertheless, both valves can be adjusted jointly, since the two intermediate links may be mounted on a common bolt.
If required for structural reasons, such as the placement of the camshaft in a desired position, one or more additional gear mechanism elements may be disposed between the cam and the intermediate link.
It is furthermore possible to adjust the intermediate links of a larger number of parallel valves jointly by one adjusting motor or mechanism, especially if these are mounted on a common bolt.
For the acceptance of a variable valve control and therefore also of the inventive device, it is of great importance to keep the adjusting power low. Because this adjusting power is higher when the device or its slip joints and joints are under load than when they are in the force-free state, which is largely the case when the valve is closed, an adjustment essentially during the common pause phases of all valves, which are to be adjusted jointly, is provided pursuant to the invention. These phases are derived from the signal of the crankshaft and the camshaft and become shorter as the number of valves, which are to be adjusted jointly, increases. The number of such valves is therefore limited.
As a result of the joint adjustment of the intake and exhaust valves in each case of only one cylinder, there are long, adjustment-friendly pause phases. However, they also enable the load of the individual cylinders to be controlled individually with an inventive adjusting strategy in such a manner that, for each load state of the engine as a whole, the torques of the individual cylinders are controlled. This is essential especially if the engine is to run quietly in the lower load range, since, due to tolerances, the valve lifts normally are not sufficiently identical. The signals, required for this adjusting strategy, are also supplied by the angle of rotation transmitter of the crankshaft and assigned to the individual cylinders by the angle of rotation transmitter of the camshaft.
Pursuant to the invention, the advantage is achieved that a reliable adjusting device for gas-exchanging valves is created with simple components. Moreover, a sensitive adjustment is advantageous attained.
The invention is now explained in greater detail by means of drawings of some examples, in which